Maître d': head waiter, dining room staff manager, or a compound butter with lemon juice and parsley: http://www.recipesource.com/side-dishes/sauces/06/rec0619.html
Mirepoix: coarse chopped onions, carrots and celery to flavor stocks, stews and other foods: http://www.ranchogordo.com/html/rg_cook_beans_primer.htm
Mise en place: literally means "to have been put in place". In the kitchen, this refers to having all your ingredients, equipment etc in order before you start cooking: http://en.wikipedia.org/wiki/Mise_en_place
Monter au beurre: finishing a sauce with butter, so as to achieve a rich flavor and velvety texture.